In general, this type of wiper unit is constructed by detachably attaching a blade on the front end of a wiper arm so that the blade can be replaced if necessary. As such attaching structures, there is, for example, a structure in that the groove width of a dent groove formed on the front end portion of the wiper arm is made into a so-called dovetail groove shape having a narrower width on the entrance side and a wider width on the inner side, while an attaching pin, which is set to a diameter approximately the same as the dimension of the groove inner side of the dent groove, is provided on a portion of the blade where the wiper arm is to be attached, and attachment is performed by fitting the dent groove onto the said attaching pin in a forcibly fitted manner.
However, in the above-described prior art, it is necessary to take measures so that the blade does not unexpectedly come off from the wiper arm, and for this purpose, a prevention against coming-off may be carried out by reducing the dimension of the groove width at the entrance side of the dent groove. In such a case, there is a problem in that inserting and drawing operation of an attaching pin with respect to the dent groove becomes troublesome during blade replacement and the operation cannot be performed easily. Furthermore, in a case where the inserting and drawing operation is repeatedly performed with a wiper arm formed of a resin material, it is assumed that the dent groove is worn or damaged. Accordingly, there is an apprehension that use of the wiper unit becomes impossible and the whole wiper unit must be replaced, thus causing a problem. These problems are solved by the present invention.